Magnetic read/write devices have magnetic recording media and magnetic heads, and data is read from/written onto the magnetic recording media by the magnetic heads. Surface-recording density must be increased in order to increase the recording capacity per unit area of each magnetic recording medium. In the modern longitudinal magnetic recording scheme, however, a decrease in the bit length of the written data causes the thermal fluctuation of magnetization of the medium, thus preventing the surface-recording density from being increased. Perpendicular magnetic recording in which a magnetizing signal is recorded in a direction perpendicular to the medium, is a type of recording scheme that can solve the above problem. There are two types of perpendicular magnetic recording schemes. One type uses a two-layer perpendicular medium having a backing soft magnetic layer, and the other type uses a single-layer perpendicular medium not having a backing soft magnetic layer. When the recording medium used is the two-layer perpendicular medium, a stronger magnetic field for recording can be applied to the medium by conducting the above signal-recording process using a so-called single magnetic pole head equipped with the main magnetic pole piece and with an auxiliary magnetic pole piece. In order to generate the magnetic field, the main magnetic pole piece is typically formed to be narrowed down in volume as the magnetic pole piece approaches an air-bearing surface, and to have a constant width in a range of several hundreds of nanometers (nm) or less in the vicinity of the air-bearing surface. The air-bearing surface of the main magnetic pole piece generally has an inverted trapezoidal shape while its width on the leading side is small in consideration of a head skew angle.
In addition to the magnetic field strength of the writing head, the magnetic field gradient in the head magnetic field perpendicular components profile where the boundaries of the write bit cells are recorded, that is, the magnetic field gradient of the head magnetic field perpendicular components profile in the traveling direction of the head, is an important factor for achieving higher recording density. To achieve higher recording density, it is necessary that the magnetic field gradient is increased. Japanese Laid-Open Patent Publication No. 2005-190518 (“Patent Document 1”) describes a structure in which a main magnetic pole piece has a trailing side shield at both a trailing side and track side of the magnetic pole piece via a non-magnetic layer in order to improve a recording magnetic field gradient.
Magnetic heads must have the appropriate recording magnetic field strength and distribution according to the particular recording medium. The magnetic field strength and distribution greatly depend on throat height. The throat height is a dimension from the medium-opposed surface to a position (diameter reduction position) at which the change rate of the width of the main magnetic pole piece in the direction of the track width from the medium-opposed surface, in the vertical direction of the element, varies at the pole tip of the main magnetic pole piece in order to concentrate magnetic fluxes at the pole tip of the main magnetic pole piece that is opposed to the medium and defines the track width. If the throat height is low, the magnetic field strength is correspondingly high and the distribution width thereof in the direction of the track width, is large. If the throat height is high, the magnetic field strength is correspondingly low and the distribution width thereof in the direction of the track width, is small. A low magnetic field strength makes it difficult to write onto media of large coercive force. If the distribution width in the direction of the track width is large, this poses the problem that data stored in adjacent tracks is erased.
In addition, to achieve a higher recording density, it is absolutely necessary to increase a track density and a linear recording density. To achieve the above, it is desirable to reduce the recording track width. For the reduction, a head having a side-shield structure, for example, is accordingly proposed. The gaps between the side shields and the main magnetic pole piece, that is, side gaps, and the film thickness of the side shields are important in the side-shield structure.
Dimensional tolerances for the throat height and for the side shields are very important and the nonuniformity of manufacturing dimensions, associated with these dimensional tolerances, must be suppressed for higher density. The nonuniformity of manufacturing dimensions deteriorates performance and reduces yield. For the throat height, the film thickness of the side shields, and the like, the causative factors of nonuniformity exist in not only wafer processes, but also a polishing process for the air-bearing surface.
For these reasons, minimizing the nonuniformity of the magnetic field strength and distribution is mandatory for improving the performance and manufacturing yield of the magnetic head. This problem must be solved to achieve even higher recording density in the magnetic disk drives that employ perpendicular magnetic recording.